Three-dimensional memory devices with architecture of increased number of bit lines

ABSTRACT

Embodiments of a three-dimensional (3D) memory device and fabrication method thereof are disclosed. The 3D memory device has an architecture with an increased number of bit lines. In an example, a stack structure is formed above a substrate. A plurality of memory strings each extending vertically through a memory region of the stack structure are formed. A plurality of bit lines are formed over the plurality of memory strings, such that at least one of the plurality of bit lines is electrically connected to a single one of the plurality of memory strings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Application Ser. No.16/402,950, filed on May 3, 2019, entitled “THREE-DIMENSIONAL MEMORYDEVICES WITH ARCHITECTURE OF INCREASED NUMBER OF BIT LINES,” which iscontinuation of International Application No. PCT/CN2019/076717, filedon Mar. 1, 2019, entitled “THREE-DIMENSIONAL MEMORY DEVICES WITHARCHITECTURE OF INCREASED NUMBER OF BIT LINES,” both of which areincorporated therein by reference in their entireties.

BACKGROUND

Embodiments of the present disclosure relate to a memory device andfabrication methods thereof.

Planar semiconductor devices, such as memory cells, are scaled tosmaller sizes by improving process technology, circuit design,programming algorithm, and fabrication process. However, as featuresizes of the semiconductor devices approach a lower limit, planarprocess and fabrication techniques become challenging and costly. Athree-dimensional (3D) device architecture can address the densitylimitation in some planar semiconductor devices, for example, flashmemory devices.

SUMMARY

Embodiments of 3D memory devices and fabrication methods thereof aredisclosed herein.

In one example, the 3D memory device includes a substrate, a pluralityof memory strings each extending vertically above the substrate in amemory region, and a plurality of bit lines over the plurality of memorystrings. At least one of the plurality of bit lines is electricallyconnected to a single one of the plurality of memory strings.

In another example, the 3D memory device includes a substrate, and aplurality of memory strings extending along a first lateral directionand a second lateral direction in a plan view. Each of the plurality ofmemory strings extends vertically above the substrate in a memoryregion. The 3D memory device also includes a plurality of bit linesextending along the second lateral direction over the plurality ofmemory strings. The plurality of bit lines are nominally parallel to oneanother. The 3D memory device also includes a cut structure overlappingwith at least one of the plurality of memory strings in the plan viewand dividing the plurality of memory strings into a first portion and asecond portion along the second lateral direction. A number of bit linesabove at least one of the plurality of memory strings is at least three.

In still another example, the 3D memory system includes a memory stack,a plurality of memory strings, a plurality of bit lines, and a pluralityof peripheral devices. The memory stack includes a plurality ofinterleaved conductor layers and insulating layers in an insulatingstructure over a substrate. The plurality of memory strings extend inthe memory stack along a first lateral direction and a second lateraldirection of a memory region in a plan view, each of the plurality ofmemory strings extending vertically into the substrate. The plurality ofbit lines are over and electrically connected to the plurality of memorystrings. In some embodiments, at least one of the plurality of bit linesis electrically connected to a single one of the plurality of memorystrings. A plurality of peripheral devices are electrically connected tothe plurality of memory strings.

In yet another example, the 3D memory system includes a memory stack, aplurality of memory strings, a cut structure, a plurality of bit lines,and a plurality of peripheral devices. The memory stack includes aplurality of interleaved conductor layers and insulating layers in aninsulating structure over a substrate. The plurality of memory stringsextend in the memory stack along a first lateral direction and a secondlateral direction in a plan view, each of the plurality of memorystrings extending vertically into the substrate. The cut structureoverlaps with at least one of the plurality of memory strings in theplan view and dividing the plurality of memory strings into a firstportion and a second portion along the second lateral direction. Theplurality of bit lines are over and electrically connected to theplurality of memory strings. The plurality of bit lines are eachparallel to one another. A number of bit lines above at least one of theplurality of memory strings is at least three. A plurality of peripheraldevices are electrically connected to the plurality of memory strings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a plan view of a 3D memory device.

FIGS. 2-4 each illustrates a plan view of an exemplary 3D memory device,according to some embodiments of the present disclosure.

FIGS. 5A-5C illustrate cross-sectional views of a 3D memory device atvarious stages of an exemplary fabrication process, according to someembodiments of the present disclosure.

FIG. 6 is a flowchart of an exemplary method for forming a 3D memorydevice, according to some embodiments of the present disclosure.

FIG. 7 illustrates a cross-sectional view of an exemplary memory systemhaving an exemplary 3D memory device, according to some embodiments ofthe present disclosure.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something). As used herein, the terms“over” and “above” are employed to describe the spatial relationshipbetween bit lines and memory strings. In some embodiments, thedescription of “a bit line over a memory string” or similar refers tothe spatial relationship of which the bit line is loosely over thememory string, and the orthogonal projections of the bit line and thememory string may or may not have overlaps on a lateral plane. In someembodiments, the description of “a bit line above a memory string” orsimilar refers to the spatial relationship of which the orthogonalprojections of the bit line and the memory string have at least partialoverlaps on a lateral plane.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or via contacts are formed) and one ormore dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND memory strings) ona laterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, thex-direction (or the x-axis) and the y-direction (or the y-axis)represent two orthogonal lateral directions. As used herein thez-direction (or the z-axis) represents a direction/axis that isperpendicular to the x-direction and the y-direction. As used herein,the term “vertical/vertically” means nominally perpendicular to thelateral surface of a substrate.

In the present disclosure, plan views are employed to depict theelectrical and spatial relationship between components (e.g., bit linesand memory strings). In some embodiments, as shown in FIGS. 2-4, theconnection between a bit line and a memory string is shown as theconnection between an upper portion (e.g., the drain) of the memorystring and the bit line in the plan view.

In a 3D memory device, GLSs divide an array region into multiple memoryregions (e.g., fingers) for data access and storage. memory strings,often arranged as an array, are distributed in a memory region, formingmemory cells for various data operations such as read, write, and erase.A memory string often includes a channel structure, a drain at an upperportion of the memory string over the channel structure, and a source ata lower portion of the memory string below the channel structure. Thesource is part of or electrically connected to an array common source(ACS) of the memory strings in the memory region. Bit lines are arrangedin parallel over the channel structures and across the GLSs. The drainis electrically connected to one of the bit lines. A memory region oftenincludes a top select gate cut (TSG cut, often includes a dielectricmaterial) that divides a memory region into two even sub-regions (e.g.,pages). A bit line is electrically connected to a memory string in onepage and another memory string in the other page so a data operation canbe performed in the memory cells of one page at a time. In a plan view,often four bit lines are arranged in a channel pitch (e.g., a lateraldistance between adjacent channel structures or between adjacent memorystrings) in each page so a bit line pitch (e.g., a lateral distancebetween two adjacent bit lines) is nominally equal to 1/4 of a channelpitch.

FIG. 1 illustrates a plan view of a 3D memory device 100. As shown inFIG. 1, in 3D memory device 100, a plurality of memory strings 108(e.g., 108-1, 108-2, and 108-3) is distributed as an array extendingalong a first lateral direction (e.g., the x-direction) and a secondlateral direction (e.g., the y-direction) in memory region 110 (e.g.,memory finger). Memory strings 108 extend vertically and laterally in amemory stack 103 of interleaved conductor layers and insulating layers.GLSs 102 extend along the first lateral direction and separate memoryregion 110 from other devices/regions. TSG cut 106 extends along thefirst lateral direction and divides memory region 110 into pages 110-1and 110-2. Each page 110-1/110-2 includes four string rows (e.g., rowsof memory strings 108) extending along the first lateral direction. In aplan view, TSG cut 106 overlaps with a string row (e.g., includingmemory string 108-3) between pages 110-1 and 110-2. A plurality of bitlines 104 extend along the second lateral direction across memory region110. Each bit line 104 is electrically connected to a memory string 108in page 110-1 and another memory string 108 in page 110-2. For example,bit line 104-1 is electrically connected in memory string 108-1 in page110-1 and memory string 108-2 in page 110-2.

As shown in FIG. 1, a channel pitch CP refers to the lateral distancebetween two adjacent memory strings 108 along a lateral direction (e.g.,the first lateral direction). A bit line pitch P0 refers to the lateraldistance between two adjacent bit lines 104 along a lateral direction(e.g., the first lateral direction). In a plan view, as shown in FIG. 1,four bit lines 104-1, 104-2, 104-3, and 104-4 are arranged in a channelpitch CP, electrically connected to four memory strings in each page110-1/110-2. Bit line pitch P0 is nominally equal to 1/4 of channelpitch CP.

3D memory device 100 can have some drawbacks. For example, the number offunctional memory strings 108 (or functional memory cells) between GLSs102 can be limited by the area occupied by TSG cut 106 and the number ofstring rows in each page 110-1/110-2. As shown in FIG. 1, TSG cut 106 islocated between pages 110-1 and 110-2, resulting in a non-functionalstring row (e.g., the string row that memory string 108-3 is located in)between pages 110-1 and 110-2. At a given time, four memory strings 108in a channel pitch CP of one page (e.g., 110-1 or 110-2) can beaccessed. A page size (e.g., data capacity) of page 110-1/110-2 islimited by bit line pitch P0, which is nominally 1/4 of channel pitchCP. One way to increase the page size is to increase the number ofmemory strings 108 along the first lateral direction. However, thisapproach can increase the dimension of the conductor layers along thefirst lateral direction, causing increased read time and program time ofthe 3D memory device.

Various embodiments in accordance with the present disclosure providearchitectures of 3D memory devices that have reduced bit line pitchesand increased bit densities, thus an increased number of bit lines inthe memory region. Bit density is herein defined as the number of databits (or data capacity) per unit area. In some embodiments, each bitline arranged in a channel pitch is electrically connected to a singlememory string in the memory region, and no TSG cut needs to be formed inthe memory region. The respective 3D memory devices may function withoutany TSG cuts, increasing the bit density of the memory region. In a planview, at least six bit lines are arranged in a channel pitch, allowingat least six memory strings to be formed in the channel pitch. Thisarchitecture can also desirably reduce the dimension of conductor layersalong the first lateral direction, thus reducing RC time constant of theconductor layers and resulting in faster read and program operations.More memory strings (or memory cells) can be accessed at a given time,increasing page size and data throughput.

In some embodiments, a 3D memory device includes one or more TSG cutsbetween GLSs and an increased number of bit lines arranged in eachchannel pitch. The TSG cuts can divide the memory region into two ormore pages. As an example, one TSG cut is formed between GLSs to formtwo pages in the memory region, and six or more bit lines can bearranged in a channel pitch. Each bit line may be electrically connectedto one memory string in one page and another memory string in the otherpage. This architecture allows six or more string rows to be accessed ata given time in the respective page, increasing bit density and pagesize. Similarly, dimension of conductor layers along the first lateraldirection can be reduced, resulting faster read and program operations.

FIG. 2 illustrates a plan view of an exemplary 3D memory device 200,according to some embodiments of the present disclosure. 3D memorydevice 200 may include a memory stack 203 that has a memory region 210(e.g., a finger), one or more slit structures 202 (e.g., GLSs) along aboundary of memory region 210, a plurality of memory strings 208 (suchas NAND memory strings) distributed in memory region 210, and aplurality of bit lines 204 arranged in parallel over memory strings 208along the second lateral direction. At least one of bit lines 204 iselectrically connected to a single memory string 208. In someembodiments, each bit line 204 is electrically to a single differentmemory string 208. In some embodiments, no TSG cut is formed in memoryregion 210 (e.g., no TSG cut overlaps with any memory strings 208 in theplan view). Memory string 208 may include a channel structure, a drainat an upper portion of memory string 208 and over the channel structure,and a source at a lower portion of memory string 208 and below thechannel structure. The source is part of or electrically connected to anACS of memory strings 208 in the memory region. The drain iselectrically connected to a respective bit line 204. Without furtherillustration, memory strings 308 and 408 depicted in FIGS. 3 and 4 havesimilar or same structures.

As shown in FIG. 2, memory strings 208 may be arranged in an arrayextending along the first lateral direction and the second lateraldirection. Memory strings 208 may be arranged in a plurality of stringrows along the second lateral direction and a plurality of stringcolumns along the first lateral direction. Bit lines 204 may extendalong the second lateral direction over memory strings 208. In someembodiments, a channel pitch CP includes N memory strings, arranged in Nstring rows along the second lateral direction. Memory strings 208 inadjacent string rows may be arranged in a staggered pattern, as shown inFIG. 2. In some embodiments, in a plan view, N bit lines are arranged inchannel pitch CP between slit structures 202. Each of the N bit lines iselectrically connected to a single different memory string 208. The Nbit lines are evenly spaced in channel pitch CP. In some embodiments, abit line pitch P1 is nominally equal to 1/N of channel pitch CP. 3Dmemory device 200 may allow memory strings 208 in memory region 210 tobe accessed at the same time during a data operation. Compared to 3Dmemory device 100, the lateral dimension of bit line 204 along the firstlateral direction is reduced, the number of bit lines in a channel pitchdoubles, and data throughput and page size each also doubles. Because noTSG cut is formed in memory region 210, bit density of 3D memory device200 may be increased by about 10% in one example.

For example, in the plan view, eight bit lines (e.g., 204-1, 204-2,204-3, 204-4, 204-5, 204-6, 204-7, and 204-8) may be arranged in channelpitch CP, over and connected to eight memory strings (e.g., 208-1,208-2, 208-3, 208-4, 208-5, 208-6, 208-7, and 208-8). In someembodiments, each bit line 204 is electrically connected to a singledifferent memory string 208. As shown in FIG. 2, bit line 204-1 iselectrically connected to memory string 208-1, bit line 204-2 iselectrically connected to memory string 208-2, . . . , bit line 204-8 iselectrically connected to memory string 208-8. Bit lines 204-1, . . . ,204-8 may be evenly spaced, and bit line pitch P1 may be nominally equalto 1/8 of channel pitch CP.

In some embodiments, four bit lines 204 are arranged above each memorystring 208. In the present disclosure, a bit line being above a memorystring can refer to the orthogonal projections of the bit line thememory string being at least partially overlapping with one another inthe lateral plane (e.g., the x-y plane). For example, bit lines 204-1,204-2, 204-3, and 204-4 may be above each of memory strings 208-1,208-2, 208-3, and 208-4; and bit lines 204-5, 204-6, 204-7, and 204-8may be above each of memory strings 208-5, 208-6, 208-7, and 208-8. Insome embodiments, bit lines 204 are formed by a multi-patterningprocess. In some embodiments, the number of bit lines 204 arranged inchannel pitch CP is determined based on design and fabricationprocesses. The number of bit lines 204 arranged in channel pitch CP maybe even or odd. In some embodiments, the number is an even integer of atleast 6. By forming more bit lines 204 in channel pitch CP, more memorystrings 208 can be accessed at a given time, increasing page size of the3D memory device.

The formation of TSG cuts is optional in this architecture. When no TSGcut is formed, finger width W1 (e.g., lateral distance between GLSsalong the second lateral direction) is reduced. At a given page size,less area in memory region 210 may be used for forming memory strings208, resulting in a reduced finger length L1 (e.g., lateral distance ofa finger along the first lateral direction). Accordingly, the dimensionof conductor layers of memory stack 203 along the first lateraldimension can be reduced, causing reduced RC time constant of theconductor layers. The device response time (e.g., response time for dataoperations such as read and program operations) can be reduced.

FIG. 3 illustrates a plan view of another 3D memory device 300,according to some embodiments of the present disclosure. 3D memorydevice 300 may include a memory stack 303 that has a memory region 310(e.g., a finger), one or more slit structures 302 (e.g., GLSs) 302 alonga boundary of memory region 310, a plurality of memory strings 308 (ormemory strings 308) distributed in memory region 310, and a plurality ofbit lines 304 arranged in parallel over memory strings 308 along thesecond lateral direction. At least one of bit lines 304 is electricallyconnected to a single memory string 308. In some embodiments, each bitline 304 is electrically to a single different memory string 308. Insome embodiments, no TSG cut is formed in memory region 310 (e.g., noTSG cut overlaps with any memory strings 308 in the plan view).

Different from 3D memory device 200, in the plan view, six bit lines 304(e.g., 304-1, 304-2, 304-3, 304-4, 304-5, and 304-6) may be arranged ina channel pitch CP, over and electrically connected to six memorystrings 308 (e.g., 308-1, 308-2, 308-3, 308-4, 308-5, and 308-6). Forexample, bit line 304-1 is electrically connected to memory string308-1, bit line 304-2 is electrically connected to memory string 308-2,. . . , bit line 304-6 is electrically connected to memory string 308-6.Bit lines 304-1, . . . , 304-6 may be evenly spaced, and a bit linepitch P2 may be nominally equal to 1/6 of channel pitch CP. In someembodiments, three bit lines 304 are arranged above each memory string308. For example, bit lines 304-1, 304-2, and 304-3 may be above each ofmemory strings 308-1, 308-2, and 308-3; and bit lines 304-5, 304-6, and304-7 may be above each of memory strings 308-4, 308-5, and 308-6. Insome embodiments, bit lines 304 are formed by a multi-patterningprocess.

Compared to 3D memory device 100, bit line pitch P2 is reduced to 1/6 ofchannel pitch CP and no TSG cut is formed in memory region 310. Fingerlength L2 and finger width W2 of memory region 310 may both be reduced.Page size and data throughout may each be increased by about 50%. Giventhe same page size, the RC time constant of conductor layers may bereduced by at least 60%. In some embodiments, bit density of 3D memorydevice 300 is similar to 3D memory device 100.

In some embodiments, no TSG cuts are formed in memory regions (e.g.,fingers) 210 and 310, and conductor layers extend continuously along thex-direction and/or the y-direction. That is, at least the firstconductor layer (e.g., the conductor on the topmost portion of theconductor layers) may extend continuously along a lateral direction itextends. In some embodiments, the first conductor layer extendscontinuously along a lateral direction it extends. In some embodiments,one or more conductor layers under the first conductor layer extendcontinuously along a lateral direction they extend. In some embodiments,all conductor layers extend continuously along a lateral direction theyextend.

FIG. 4 illustrates a plan view of another 3D memory device 400,according to some embodiments of the present disclosure. 3D memorydevice 400 may include a memory stack 403 that has a memory region 410,one or more slit structures (or GLSs) 402 along a boundary of memoryregion 410, a plurality of memory strings 408 (or memory strings 408)distributed in memory region 410, a TSG cut 406 (or cut structure)extending along the first lateral direction, and a plurality of bitlines 404 arranged in parallel over memory strings 408 along the secondlateral direction. TSG cut 406 may divide memory region 410 into memorysub-regions (410-1 and 410-2 (e.g., memory pages), each including aportion of the array of memory strings 408. In some embodiments, in theplan view, TSG cut 406 overlaps with a string row along the secondlateral direction and divides the array of memory strings 408 into twoeven portions (e.g., two portions with the same number of memory strings408 and/or same/symmetric arrangement of memory strings 408).

In some embodiments, in the plan view, each bit line 404 is electricallyconnected to one memory string 408 in memory sub-region 410-1 andanother memory string 408 in memory sub-region 410-2. Each memory string408 in the same memory sub-region 410-1/410-2 may be electricallyconnected to a different bit line 404. In the plan view, N bit lines arearranged in channel pitch CP. The number of memory strings 408 arrangedin channel pitch in each memory sub-region 410-1/410-2 (e.g., betweenGLS 402 and TSG cut 406) may be equal to N. N may be at least 6. In someembodiments, the N bit lines are evenly arranged in channel pitch CP,and a bit line pitch P3 is nominally equal to 1/N of channel pitch CP.In some embodiments, memory region 410 includes 13 string rows, and eachof memory sub-regions 410-1 and 410-2 includes six string rows extendingalong the second lateral direction. In some embodiments, 3 bit lines areabove each memory string 408 in the plan view.

For example, as shown in FIG. 4, bit lines 404-1, 404-2, 404-3, 404-4,404-5, and 404-6 may be arranged in channel pitch CP and over memorystrings 408-1, 408-2, . . . , and 408-6 in memory sub-region 410-1 andmemory strings 408-7, 408-8, . . . , and 408-12 in memory sub-region410-2. Bit line 404-1 may be electrically connected to memory strings408-1 and 408-12, bit line 404-2 may be electrically connected to memorystrings 408-2 and 408-11, bit line 404-3 may be electrically connectedto memory strings 408-3 and 408-10, bit line 404-4 may be electricallyconnected to memory strings 408-4 and 408-9, bit line 404-5 may beelectrically connected to memory strings 408-5 and 408-8, and bit line404-6 may be electrically connected to memory strings 408-6 and 408-7.In some embodiments, bit lines 404-1, 404-2, and 404-3 may be above eachof memory strings 408-1, 408-2, 408-3, 408-10, 408-11, and 408-12. Insome embodiments, bit lines 404-4, 404-8, and 404-6 may be above each ofmemory strings 408-4, 408-5, 408-6, 408-7, 408-8, and 408-9.

Compared to 3D memory device 100, bit line pitch P3 is reduced to 1/6 ofchannel pitch CP and TSG cut is formed in memory region 410. Page sizeand data throughout may each be increased by about 50%. In someembodiments, bit density of 3D memory device 400 is increased by about10% compared to 3D memory device 100.

FIGS. 5A-5C illustrate cross-sectional views of a 3D memory device atvarious stages of an exemplary fabrication process, according to someembodiments of the present disclosure. FIG. 6 is a flowchart describingfabrication method 600 that forms a 3D memory device. The specific orderand fabrication methods of operations 602-608 are subjected to differentdesigns and fabrication requirements, and should not be limited by theembodiments of the present disclosure. FIG. 7 is an exemplary system 700(e.g., a bonded semiconductor device) that includes a 3D memory devicedescribed in the present disclosure.

It is noted that x and y axes/directions are included in FIGS. 5A-5C andFIG. 7 to further illustrate the spatial relationship of the componentsin 3D memory device having a substrate 502 and system 700 having asubstrate 708. Substrate 502 and substrate 708 each includes two lateralsurfaces (e.g., a top surface and a bottom surface) extending laterallyin the x-direction (i.e., the lateral direction). As used herein,whether one component (e.g., a layer or a device) is “on,” “above,” or“below” another component (e.g., a layer or a device) of a semiconductordevice (e.g., 3D memory device or bonded semiconductor device) isdetermined relative to the substrate of the semiconductor device (e.g.,substrate 502 or substrate 708) in the y-direction (i.e., the verticaldirection) when the substrate is positioned in the lowest plane of thesemiconductor device in the y-direction. The same notion for describingspatial relationship is applied throughout the present disclosure.

Referring to FIG. 6, method 600 includes operation 602, in which adielectric stack is formed on a substrate. The substrate which caninclude silicon (e.g., single crystalline silicon), silicon germanium(SiGe), gallium arsenide (GaAs), germanium (Ge), silicon on insulator(SOI), or any other suitable materials. The dielectric stack can includea plurality of dielectric/sacrificial layer pairs.

As illustrated in FIG. 5A, pairs of a first dielectric layer 510 and asecond dielectric layer (known as a “sacrificial layer”) 512 (togetherreferred to herein as “dielectric layer pairs”) are formed over asubstrate 502. The stacked dielectric layer pairs can form a dielectricstack 508. In some embodiments, an isolation layer 504, such as asilicon oxide film, is formed between substrate 502 and dielectric stack508. Dielectric stack 508 can include an alternating stack ofsacrificial layer 512 and dielectric layer 510 that is different fromsacrificial layer 512. In some embodiments, each dielectric layer pairincludes a layer of silicon nitride and a layer of silicon oxide. Insome embodiments, sacrificial layers 512 can each have the samethickness or have different thicknesses. Similarly, dielectric layers510 can each have the same thickness or have different thicknesses.Isolation layer 504 and dielectric stack 508 can be formed by one ormore thin film deposition processes including, but not limited to,chemical vapor deposition (CVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), or any combination thereof.

Method 600 proceeds to operation 604, as illustrated in FIG. 6, in whicha plurality of memory strings each extending vertically through thedielectric stack are formed. As illustrated in FIG. 5B, memory strings514 are formed on substrate 502, each of which extends verticallythrough dielectric stack 508 and above substrate 502. In someembodiments, each memory string 514 can include a lower semiconductorplug 506 and an upper semiconductor plug 507 at its lower portion andupper portion, respectively. Lower semiconductor plug 506 can be atleast part of the source of memory string 514 (e.g., ACS of the memorystrings in the respective memory region). In some embodiments,fabrication processes to form memory string 514 include etching achannel hole through dielectric stack 508 and forming lowersemiconductor plug 506 at the lower portion of the channel hole. Thechannel hole can be formed by dry etching and/or wet etching, such asdeep reactive ion etching (RIE), and lower semiconductor plug 506 can beepitaxially grown from substrate 502 into the lower portion of thechannel hole.

In some embodiments, fabrication processes to form memory string 514also include forming a memory film 516 along the sidewalls of thechannel hole. Memory film 516 can be a combination of multipledielectric layers including, but not limited to, a tunneling layer, astorage layer, and a blocking layer. Tunneling layer can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, silicon oxynitride, or any combination thereof. Storagelayer can include materials for storing charge for memory operation. Thestorage layer materials can include, but not limited to, siliconnitride, silicon oxynitride, a combination of silicon oxide and siliconnitride, or any combination thereof. The blocking layer can includedielectric materials including, but not limited to, silicon oxide or acombination of silicon oxide/silicon oxynitride/silicon oxide (ONO). Theblocking layer can further include a high-k dielectric layer, such as analuminum oxide layer.

In some embodiments, fabrication processes to form memory string 514also include forming a semiconductor channel 518 over memory film 516and forming a filling layer 520 over semiconductor channel 518 topartially or fully fill the remaining space of the channel hole.Semiconductor channel 518 can include semiconductor materials, such aspolysilicon. Filling layer 520 can include dielectric materials, such assilicon oxide. Filling layer 520, semiconductor channel 518, and memoryfilm 516 can be formed by processes such as ALD, CVD, PVD, any othersuitable processes, or any combination thereof.

In some embodiments, upper semiconductor plug 507 is formed at the upperportion of memory string 514 as the drain of memory string 514. Uppersemiconductor plug 507 can be formed by etching back the upper portionof memory string 514 by dry etching and/or wet etching, followed by oneor more deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof, to deposit a semiconductormaterial, such as polysilicon, into the recess formed by theetching-back process.

Method 600 proceeds to operation 606, as illustrated in FIG. 6, in whicha memory stack is formed from the dielectric stack and slit structure isformed in the memory stack. As illustrated in FIG. 5C, a slit structure530 is formed to extend vertically in a memory stack 528 formed fromdielectric stack 508. Slit structure 530, corresponding to the slitstructures 202, 302, and 402 depicted in FIGS. 2-4, may include adielectric structure 532 and a source contact 534 in dielectricstructure 532. Source contact 534 may extend to substrate 502 and beelectrically connected to the ACS of memory strings 514. In someembodiments, dielectric stack 508 is repetitively etched to form astaircase structure of dielectric/sacrificial layer pairs. A slitopening may be formed in the staircase structure, exposing substrate502. The slit opening may correspond to slit structure 530. The etchedsacrificial layers may then be replaced, with a plurality of conductorlayers, in the dielectric/sacrificial layer pairs through the slitopening to form a plurality of conductor/dielectric layer pairs (e.g.,510-2/512-2). The conductor layers 512-2 may include any suitableconductive material such as tungsten, copper, aluminum, and/or cobalt.In some embodiments, the slit opening is filled with a dielectricmaterial, and a conductive material is formed in the dielectricmaterial, forming dielectric structure 532 and source contact 534.Source contact may be electrically connected to the ACS of memorystrings 514. The dielectric structure may include any suitabledielectric materials such as silicon oxide, silicon nitride, and/orsilicon oxynitride. The source contact may be made of any suitableconductive material such as tungsten, copper, cobalt, aluminum, silicon,and/or silicides. In some embodiments, word line via contacts (or viacontacts) that are electrically connected to conductor layers 512-2 areformed.

Method 600 proceeds to operation 608, as illustrated in FIG. 6, in whicha plurality of bit lines are formed over the memory strings. In someembodiments, at least one of the plurality of bit lines is electricallyconnected to a single one of the plurality of memory strings. In someembodiments, at least three bit lines are above one memory string. Anarray interconnect layer, including a plurality of interconnects in oneor more inter-layer dielectric (ILD) layers, may be formed. Asillustrated in FIG. 5C, an array interconnect layer 522 can be formedabove dielectric stack 508 and memory strings 514. Array interconnectlayer 522 can include interconnects, such as bit lines 524, in one ormore ILD layers for transferring electrical signals to and from memorystrings 514. In some embodiments, bit line contacts 526 can be formed inan ILD layer formed above memory stack 528 prior to forming arrayinterconnect layer 522, such that each bit line contact 526 is above andin contact with upper semiconductor plug 507 (the source) ofcorresponding memory string 514 and is below and in contact withcorresponding bit line 524. In some embodiments, the arrangement andlayout of bit line 524 may be referred to the description of bit lines204, 304, and 404 in FIGS. 2-4 and is not repeated herein.

In some embodiments, array interconnect layer 522 includes multiple ILDlayers and interconnects therein formed in multiple processes. Forexample, bit lines 524 can include conductive materials deposited by oneor more thin film deposition processes including, but not limited to,CVD, PVD, ALD, electroplating, electroless plating, or any combinationthereof. Fabrication processes to form bit lines 524 can also includephotolithography, chemical mechanical polishing (CMP), wet/dry etch, orany other suitable processes. The ILD layers can include dielectricmaterials deposited by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, or any combinationthereof. The ILD layers and interconnects illustrated in FIG. 5C can becollectively referred to as an “interconnect layer” (e.g., arrayinterconnect layer 522).

The formed memory stack may be coupled with other parts of a memorysystem for operations such as read, write, and erase. FIG. 7 illustratesa cross-sectional view of a system 700 that includes the 3D memorydevice formed by fabrication method 600. System 700 may include a bondedsemiconductor device.

System 700 represents an example of a memory system that includes a 3Dmemory device, according to embodiments of the present disclosure.System 700 can include a substrate 708, which can include silicon (e.g.,single crystalline silicon), silicon germanium (SiGe), gallium arsenide(GaAs), germanium (Ge), silicon on insulator (SOI), or any othersuitable materials. System 700 can include two semiconductor structures,i.e., a memory array device chip 702 that includes a 3D memory devicedescribed in any of FIGS. 2-4 and a peripheral device chip 704 bonded ontop of memory array device chip 702 in a face-to-face manner at abonding interface 706. It should be noted that peripheral device chip704 is used herein merely as an example for illustration of componentsof the system. In some embodiments, peripheral devices are formed on thesame substrate as the 3D memory device, either stack above or below the3D memory device or on the side of the 3D memory device. In someembodiments, bonding interface 706 is disposed between memory arraydevice chip 702 and peripheral device chip 704 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 706 is the placeat which memory array device chip 702 and peripheral device chip 704 aremet and bonded. In practice, bonding interface 706 can be a layer with acertain thickness that includes the top surface of memory array devicechip 702 and the bottom surface of peripheral device chip 704.

In some embodiments, memory array device chip 702 is a NAND Flash memorydevice in which memory cells are provided in the form of an array ofmemory strings 710 (e.g., NAND memory strings) in a memory array devicelayer 734. Memory array device layer 734 can be disposed on substrate708. In some embodiments, each memory string 710 extends verticallythrough a plurality of pairs each including a conductor layer and adielectric layer (referred to herein as “conductor/dielectric layerpairs”). The stacked conductor/dielectric layer pairs are collectivelyreferred to herein as a memory stack 712 in memory array device layer734. The conductor layers and dielectric layers in memory stack 712 canstack alternatingly in the vertical direction. Each memory string 710can include a semiconductor channel and a composite dielectric layer(also known as a “memory film”) including a tunneling layer, a storagelayer (also known as a “charge trap/storage layer”), and a blockinglayer (not shown). The structure of memory strings 710 may be the sameas or similar to memory strings 514 described in FIG. 514, and thelateral arrangement of memory strings 710 may be referred to the lateralarrangement of semiconductor channels/memory strings (e.g., 208, 308,and 408) described in FIGS. 2-4. In some embodiments, memory arraydevice layer 734 further includes a gate line slit (“GLS”) or slitstructure 714 that extends vertically through memory stack 712. GLS 714can be used to form the conductor/dielectric layer pairs in memory stack712 by a gate replacement process and can be filled with conductivematerials for electrically connecting ACS of memory strings 710.

In some embodiments, memory array device chip 702 also includes an arrayinterconnect layer 736 above memory array device layer 734 fortransferring electrical signals to and from memory strings 710. As shownin FIG. 7, array interconnect layer 736 can include a plurality ofinterconnects (also referred to herein as “contacts”), includingvertical interconnect access (via) contacts 716 and lateral interconnectlines 718. As used herein, the term “interconnects” can broadly includeany suitable types of interconnects, such as middle-end-of-line (MEOL)interconnects and back-end-of-line (BEOL) interconnects. Arrayinterconnect layer 736 can further include one or more interlayerdielectric (ILD) layers (also known as “intermetal dielectric (IMD)layers”) in which bit lines 746, bit line contacts 748, interconnectlines 718, and via contacts 716 can form. Bit line contact 748 may bepositioned between bit line 746 and memory string 710. Bit line contact748 may be electrically connected to bit line 746 and an upper portionof memory string 710 (e.g., drain of memory string 710) to transmitsignals/data between bit line 746 and memory string 710. Detaileddescription of bit lines 746 may be referred to the description of bitlines in FIGS. 2-4 and is not repeated herein.

As shown in FIG. 7, memory array device chip 702 can further include abonding layer 738 at bonding interface 706 and above array interconnectlayer 736 and memory array device layer 734. Bonding layer 738 caninclude a plurality of bonding contacts 730 and dielectrics electricallyisolating bonding contacts 730. Bonding contacts 730 can includeconductive materials including, but not limited to, tungsten, cobalt,copper, aluminum, silicides, or any combination thereof. The remainingarea of bonding layer 738 can be formed with dielectrics including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, or any combination thereof. Bonding contacts 730 andsurrounding dielectrics in bonding layer 738 can be used for hybridbonding.

Peripheral device chip 704 can include a plurality of transistors 722 ina peripheral device layer 740 disposed below a semiconductor layer 720,such as a thinned substrate. In some embodiments, peripheral devicelayer 740 can include any suitable digital, analog, and/or mixed-signalperipheral devices used for facilitating the operation of system 700.For example, the peripheral devices can include one or more of a pagebuffer, a decoder (e.g., a row decoder and a column decoder), a senseamplifier, a driver, a charge pump, a current or voltage reference, orany active or passive components of the circuits (e.g., transistors,diodes, resistors, or capacitors). The peripheral devices in peripheraldevice layer 740 can be electrically connected to memory strings 710through one or more layers of interconnects.

Similar to memory array device chip 702, peripheral device chip 704 canalso include a peripheral interconnect layer 742 disposed belowperipheral device layer 740 for transferring electrical signals to andfrom transistors 722. Peripheral interconnect layer 742 can include aplurality of interconnects, including interconnect lines 726 and viacontacts 724 in one or more ILD layers. In some embodiments, peripheraldevice chip 704 also includes via contacts 728 (e.g., through siliconvias (TSVs) if semiconductor layer 720 is a thinned silicon substrate)extending vertically through semiconductor layer 720. In someembodiments, peripheral device chip 704 further includes a BEOLinterconnect layer (not shown) above transistors 722 and semiconductorlayer 720. In some embodiments, the BEOL interconnect layer includes anysuitable BEOL interconnects and contact pads that can transferelectrical signals between system 700 and external circuits.

As shown in FIG. 7, peripheral device chip 704 can further include abonding layer 744 at bonding interface 706 and below peripheralinterconnect layer 742 and peripheral device layer 740. Bonding layer744 can include a plurality of bonding contacts 732 and dielectricselectrically isolating bonding contacts 732. Bonding contacts 732 caninclude conductive materials including, but not limited to, tungsten,cobalt, copper, aluminum, silicides, or any combination thereof. Theremaining area of bonding layer 744 can be formed with dielectricsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, low-k dielectrics, or any combination thereof. Bondingcontacts 732 and surrounding dielectrics in bonding layer 744 can beused for hybrid bonding.

Embodiments of the present disclosure provide a 3D memory device. Insome embodiments, the 3D memory device includes a substrate, a pluralityof memory strings each extending vertically above the substrate in amemory region, and a plurality of bit lines over the plurality of memorystrings. At least one of the plurality of bit lines is electricallyconnected to a single one of the plurality of memory strings.

In some embodiments, each one of the plurality of memory strings iselectrically connected to a single different one of the plurality of bitlines.

In some embodiments, the 3D memory device further includes at least oneslit structure extending laterally along a boundary of the memoryregion.

In some embodiments, the plurality of memory strings are arranged in anarray extending along a first lateral direction and a second lateraldirection in the memory region. The first lateral direction may beperpendicular to the second lateral direction. The plurality of bitlines may be arranged along the first direction and extends along thesecond lateral direction, being parallel with one another. In a planview, a number of bit lines arranged in a channel pitch along the firstlateral direction may be equal to a number of memory stringselectrically connected to the bit lines along the second lateraldirection.

In some embodiments, the array is arranged between two slit structureseach laterally extending along the first direction. In the plan view,the number of bit lines arranged in the channel pitch may be equal tothe number of memory strings in the channel pitch and between the twoslit structures.

In some embodiments, in the plan view, the bit lines in the channelpitch are evenly spaced, a bit line pitch along the first lateraldirection being nominally equal to 1/N of the channel pitch. N may beequal to the number of bit lines in the channel pitch.

In some embodiments, the array includes at least six string rows alongthe second lateral direction.

In some embodiments, N is a positive even integer.

In some embodiments, the plurality of memory strings each includes achannel structure and a drain over the channel structure. The drain maybe electrically connected to a respective bit line.

In some embodiments, in a plan view, no cut structure overlaps with theplurality of memory strings in the memory region, the memory regionbeing a finger.

In some embodiments, the 3D memory device further includes a pluralityof interleaved conductor layers and insulating layers extendinglaterally and intersecting with the plurality of memory strings. A firstconductor layer may extend continuously along a direction it extends inthe memory region.

Embodiments of the present disclosure also provide another 3D memorydevice. The 3D memory device includes a substrate, and a plurality ofmemory strings extending along a first lateral direction and a secondlateral direction in a plan view. Each of the plurality of memorystrings extends vertically above the substrate in a memory region. The3D memory device also includes a plurality of bit lines extending alongthe second lateral direction over the plurality of memory strings. Theplurality of bit lines is nominally parallel to one another. The 3Dmemory device also includes a cut structure overlapping with at leastone of the plurality of memory strings in the plan view and dividing theplurality of memory strings into a first portion and a second portionalong the second lateral direction. A number of bit lines above at leastone of the plurality of memory strings is at least three.

In some embodiments, the first portion and the second portion of theplurality of memory strings includes a same number of string rows alongthe second lateral direction and a same number of string columns alongthe first lateral direction. Each one of the plurality of bit lines maybe electrically connected to one memory string in the first portion andanother memory string in the second portion.

In some embodiments, the plurality of memory strings are arranged in anarray extending along the first lateral direction and the second lateraldirection, and each of the first portion and the second portion of theplurality of memory strings includes an even number of string rows alongthe second lateral direction.

In some embodiments, each of the first portion and the second portionincludes N string rows along the second lateral direction, and a channelpitch includes N bit lines arranged along the first lateral direction. Abit line pitch may be nominally 1/N of the channel pitch along the firstlateral direction. N may be equal to at least 6.

In some embodiments, N is a positive even integer.

In some embodiments, the plurality of memory strings each includes achannel structure and a drain over the channel structure, the drainbeing electrically connected to a respective bit line.

Embodiments of the present disclosure provide a 3D memory system. The 3Dmemory system includes a memory stack, a plurality of memory strings, aplurality of bit lines, and a plurality of peripheral devices. Thememory stack may include a plurality of interleaved conductor layers andinsulating layers in an insulating structure over a substrate. Theplurality of memory strings may extend in the memory stack along a firstlateral direction and a second lateral direction in a plan view, each ofthe plurality of memory strings extending vertically into the substrate.The plurality of bit lines may be over and electrically connected to theplurality of memory strings. In some embodiments, at least one of theplurality of bit lines is electrically connected to a single one of theplurality of memory strings. A plurality of peripheral devices may beelectrically connected to the plurality of memory strings.

In some embodiments, each one of the plurality of memory strings iselectrically connected to a single different one of the plurality of bitlines.

In some embodiments, the 3D memory system further includes at least oneslit structure laterally extending along a boundary of the memoryregion.

In some embodiments, the plurality of memory strings is arranged in anarray extending along the first lateral direction and the second lateraldirection in the memory region. The first lateral direction may beperpendicular to the second lateral direction. In some embodiments, theplurality of bit lines is arranged along the first direction and extendsalong the second lateral direction, being parallel with one another. Inthe plan view, a number of bit lines arranged in a channel pitch alongthe first lateral direction may be equal to a number of memory stringselectrically connected to the bit lines along the second lateraldirection.

In some embodiments, the array is arranged between two slit structureseach laterally extending along the first direction. In some embodiments,in the plan view, the number of bit lines arranged in the channel pitchis equal to the number of memory strings in the channel pitch andbetween the two slit structures.

In some embodiments, in the plan view, the bit lines in the channelpitch are evenly spaced. A bit line pitch along the first lateraldirection may be nominally equal to 1/N of the channel pitch, N beingequal to the number of bit lines in the channel pitch.

In some embodiments, the array includes at least six string rows alongthe second lateral direction.

In some embodiments, N is a positive even integer.

In some embodiments, the plurality of memory strings each includes achannel structure and a drain over the channel structure. The drain maybe electrically connected to a respective bit line.

In some embodiments, in a plan view, no cut structure overlaps with theplurality of memory strings in the memory region, the memory regionbeing a finger.

In some embodiments, the first conductor layer extends continuouslyalong a direction it extends in the memory region.

Embodiments of the present disclosure provide a 3D memory system. The 3Dmemory system includes a memory stack, a plurality of memory strings, acut structure, a plurality of bit lines, and a plurality of peripheraldevices. The memory stack may include a plurality of interleavedconductor layers and insulating layers in an insulating structure over asubstrate. The plurality of memory strings may extend in the memorystack along a first lateral direction and a second lateral direction ina plan view, each of the plurality of memory strings extendingvertically into the substrate. The cut structure may overlap with atleast one of the plurality of memory strings in the plan view anddividing the plurality of memory strings into a first portion and asecond portion along the second lateral direction. The plurality of bitlines may be over and electrically connected to the plurality of memorystrings. The plurality of bit lines may each be parallel to one another.A number of bit lines above at least one of the plurality of memorystrings may be at least three. A plurality of peripheral devices may beelectrically connected to the plurality of memory strings.

In some embodiments, the first portion and the second portion of theplurality of memory strings include a same number of string rows alongthe second lateral direction and a same number of string columns alongthe first lateral direction. In some embodiments, each one of theplurality of bit lines is electrically connected to one memory string inthe first portion and another memory string in the second portion.

In some embodiments, the plurality of memory strings are arranged in anarray extending along the first lateral direction and the second lateraldirection. In some embodiments, each of the first portion and the secondportion of the plurality of memory strings includes an even number ofstring rows along the second lateral direction.

In some embodiments, in the plan view, each of the first portion and thesecond portion includes N string rows along the second lateraldirection. A channel pitch may include N bit lines arranged along thefirst lateral direction. A bit line pitch may be nominally 1/N of thechannel pitch along the first lateral direction, N being equal to atleast 6.

In some embodiments, N is a positive even integer.

In some embodiments, the plurality of memory strings each includes achannel structure and a drain over the channel structure, the drainbeing electrically connected to a respective bit line.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a three-dimensional (3D)memory device, comprising: forming a stack structure above a substrate;forming a plurality of memory strings each extending vertically througha memory region of the stack structure; and forming a plurality of bitlines over the plurality of memory strings, such that at least one ofthe plurality of bit lines is electrically connected to a single one ofthe plurality of memory strings.
 2. The method of claim 1, whereinforming the stack structure comprising forming a dielectric stackcomprising stacked dielectric layer pairs; and the method furthercomprises after forming the plurality of memory strings, forming amemory stack from the dielectric stack, such that the plurality ofmemory strings each extends vertically through the memory region of thememory stack.
 3. The method of claim 2, wherein the memory stackcomprises a plurality of interleaved conductive layers and insulatinglayers extending laterally and intersecting with the plurality of memorystrings; in a plan view, no cut structure overlaps with the plurality ofmemory strings in the memory region, the memory region being a finger;and a first conductor layer extends continuously along a direction itextends in the memory region.
 4. The method of claim 1, wherein each oneof the plurality of memory strings is electrically connected to a singledifferent one of the plurality of bit lines.
 5. The method of claim 1,further comprising forming at least one slit structure extendinglaterally along a boundary of the memory region.
 6. The method of claim5, wherein the plurality of memory strings are arranged in an arrayextending along a first lateral direction and a second lateral directionin the memory region, the first lateral direction being perpendicular tothe second lateral direction; and the plurality of bit lines arearranged along the first direction and extends along the second lateraldirection, being parallel with one another.
 7. The method of claim 6,wherein in a plan view, a number of bit lines arranged in a channelpitch along the first lateral direction is equal to a number of memorystrings electrically connected to the bit lines along the second lateraldirection.
 8. The method of claim 6, wherein the array is arrangedbetween two slit structures each laterally extending along the firstdirection; and in the plan view, the number of bit lines arranged in thechannel pitch is equal to the number of memory strings in the channelpitch and between the two slit structures.
 9. The method of claim 8,wherein in the plan view, the bit lines in the channel pitch are evenlyspaced, a bit line pitch along the first lateral direction beingnominally equal to 1/N of the channel pitch, N being equal to the numberof bit lines in the channel pitch.
 10. The method of claim 6, whereinthe array comprises at least six string rows along the second lateraldirection.
 11. The method of claim 10, wherein N is a positive eveninteger.
 12. The method of claim 1, wherein forming the plurality ofmemory strings comprising, for each of the memory strings, forming achannel structure and a drain over the channel structure, the drainbeing electrically connected to a respective bit line.